1. Field of the Invention
The present invention relates to a phase compensation circuit which is incorporated into a radar system or a communication system in a microwave band to compensate change in phase due to the temperature of these devices, and a frequency converter device using the phase compensation circuit, and an active phased array antenna using the phase compensation circuit or the frequency converter device.
2. Description of the Related Art
In the radar system, the communication system, etc., the active phased array antenna consisting of a plurality of element antennas is employed as the antenna used therein from viewpoints such as reliability and a high speed operation, and also a transmitting module or a receiving module for amplifying or controlling the signal is employed in each element antenna.
Since the modules each has uniform phase including a temperature characteristic are requested particularly as these modules, normally the phase shifter for compensating variation in phase is incorporated in each module.
FIG. 15 is a view showing the phase shifter in the prior art, which is disclosed in the MICROWAVE JOURNAL, 1989, STATE OF ART REFERENCE, pp. 109, for example. In FIG. 15, 1 is a coupler; 2, an input terminal; 3, an output terminal; 4, a coupling terminal; 5, a passing terminal; 6, a capacitor; 7, a variable capacity element; 8, a choke circuit; and 9, a direct current power supply.
In this phase shifter, a series circuit of the capacitor 6 and the variable capacity element 7 is provided between the coupling terminal 4 of a coupler 1 having four terminals and ground and the passing terminal of the coupler 1 and ground respectively. Then, in order to apply a desired bias from the direct current power supply 9 to each variable capacity element 7, the choke circuit 8 is connected to the variable capacity element 7.
Also, a coupler such as a branch line coupler, an interdigital coupler, or the like, which can distribute the microwave signal to the coupling terminal 4 and the passing terminal 5 at the same amplitude to have phase difference of 90 degree between both terminals, is employed as the coupler 1. Also, a varactor diode, an FET (Field Effect Transistor), or the like, whose capacitance is changed depending on its applied voltage, is employed as the variable capacity element 7. Further, in order not to affect the microwave characteristic of the phase shifter as much as possible, the choke circuit 8 is designed to have a high impedance in a desired frequency band. Moreover, the capacitor 6 for preventing the direct current is selected to have a value which can yield as low impedance as possible in the microwave band.
Next, an operation of the phase shifter will be explained hereunder. The microwave signal which is input from the input terminal 2 is distributed to the coupling terminal 4 and the passing terminal 5 to have the same amplitude and the phase difference of 90 degree between both terminals respectively. The distributed microwave signal is supplied to the variable capacity element 7 via the capacitor 6. Normally the impedance of the variable capacity element 7 substantially consists of a reactance component only since its resistance component is small, and therefore the microwave signal supplied to the variable capacity element 7 is totally reflected there toward the coupler 1 side. In addition, the reflected microwave signals are synthesized oppositely in phase at the input terminal 2 and also synthesized commonly in phase at the output terminal 3, and as a result such microwave signal fully appears on the output terminal 3.
In this case, the phase of the microwave signal being reflected by the variable capacity element 7 largely depends upon a capacitance of the variable capacity element 7. Thus, the larger a degree of change in the capacitance is increased, the larger a degree of change in the phase is increased.
FIGS. 16A to 16C show an example of the microwave characteristic of the phase shifter shown in FIG. 15. In general, the capacitance of the variable capacity element 7 is decreased smaller as the voltage VR of the direct current power supply 9 applied to the variable capacity element 7 is increased higher, so that the phase of the reflected microwave signal leads.
Therefore, as shown in FIG. 16A, the phase shifter shows the right-upward inclined phase characteristic if an angular frequency xcfx89 is kept constant. Also, as shown in FIG. 16B, VSWR at the input terminal 2 does not depend on the voltage VR and thus shows the good value since the reflected microwave signals are always synthesized oppositely in phase at the input terminal 2. Further, as shown in FIG. 16C, the frequency characteristic of VSWR always shows the good value if the voltage VR is kept constant.
The phase of the microwave signal from the input terminal 2 to the output terminal 3 can be changed by varying the voltage VR of the direct current power supply 9 in this manner. For this reason, even though the phase characteristics of the amplifier, the mixer, etc. employed in the individual transmitting module or receiving module relative to the temperature are different, the phase compensation can be achieved by using this phase shifter. As a result, the transmitting modules or the receiving modules which can suppress the change in phase relative to the temperature and have the uniform phase characteristic can be implemented.
FIG. 17 is a block diagram showing one constituent element of an active phased array antenna to which the transmitting module having the phase shifter in the prior art shown in FIG. 15 is applied. In FIG. 17, a reference 10 denotes a gain compensation circuit using a variable attenuator; 11, a phase shifter in the prior art; 12, a high-frequency amplifier using semiconductor; 13, a transmitting module which consists of the gain compensation circuit 10, the phase shifter 11, and the high-frequency amplifier 12; and 14, an element antenna.
Therefore, the signal input from the input terminal 2 is passed through the gain compensation circuit 10 and the phase shifter 11, then amplified by the high-frequency amplifier 12, and then irradiated into a space from the element antenna 14.
A large number of constituent elements, each consists of such transmitting module 13 and the element antenna 14, are employed in the active phased array antenna. Thus, a very high output can be obtained by spatially synthesizing the signal which is transmitted from the element antenna 14.
In this case, the active phased array antenna for transmission is disclosed herein. A large number of receiving modules and the element antennas 14 are also employed in the active phased array antenna for reception.
According to the phase shifter in the prior art shown in FIG. 15, since the interdigital coupler is normally employed as the coupler 1, the wideband characteristic of about 1 octave can be derived.
However, such wideband is not necessary for the transmitting modules 13 or the receiving modules which are employed in the active phased array antenna. In many cases, the lower cost and the reduction in size of the module are requested rather than the wider bandwidth. In the phase shifter 11 in the prior art, there has been such a problem that, since two expensive variable capacity elements 7 are needed and also the coupler 1 having a length of xc2xcxcex in the predetermined frequency band is employed, the cost and the size of the transmitting modules 13 or the receiving modules are increased.
Further, there has been another problem that the cost and the weight of the active phased array antenna, to which the transmitting modules 13 or the receiving modules are applied, are increased.
The present invention has been made to overcome above subjects and it is an object of the present invention to provide a phase compensation circuit which is capable of compensating the phase relative to the temperature with a simple configuration employing one variable capacity element, and a frequency converter device using the phase compensation circuit, and an active phased array antenna to which the phase compensation circuit or the frequency converter device is applied.
The phase compensation circuit according to a first aspect of the invention comprises two first inductive elements connected in series with a main line through which a signal is passed; a series circuit consisting of a capacitor and a variable capacity element, which are provided between a connecting point between the first inductive elements and ground; a second inductive element connected in parallel with the series circuit; and a choke circuit connected between the capacitor and the variable capacity element of the series circuit.
Also, in the phase compensation circuit according to a second aspect of the invention, an inductive element whose inductance can be varied is employed as the second inductive element.
Also, the phase compensation circuit according to a third aspect of the invention further comprises a third inductive element provided between the capacitor and the variable capacity element of the phase compensation circuit disclosed in the above first invention.
Also, the phase compensation circuit according to a fourth aspect of the invention comprises a series circuit consisting of a capacitor and a variable capacity element, which are provided between a main line through which a signal is passed and ground; a choke circuit connected between the capacitor and the variable capacity element of the series circuit; an inductor connected in series with the main line; and a capacitor provided between the inductor and ground.
Also, the phase compensation circuit according to a fifth aspect of the invention comprises a series circuit consisting of a xc2xcxcex line, a capacitor, an impedance compensation line, and a variable capacity element, which are provided between a main line through which a signal is passed and ground; and a choke circuit connected between the impedance compensation line and the variable capacity element of the series circuit.
Also, the phase compensation circuit according to a sixth aspect of the invention comprises a series circuit consisting of an inductive line, a capacitor, an impedance compensation line, and a variable capacity element, which are provided between a main line through which a signal is passed and ground; a capacitive element connected to the inductive line; and a choke circuit connected between the impedance compensation line and the variable capacity element of the series circuit.
Also, the frequency converter device according to a seventh aspect of the invention comprises the phase compensation circuit which is set forth in any one of claims 1 to 6 and employed in a local signal system of the frequency converter device.
Also, the active phased array antenna according to an eighth aspect of the invention comprises transmitting modules or receiving modules each of which includes the phase compensation circuit set forth in any one of above respective aspects of the invention.
Also, the active phased array antenna according to the ninth invention comprises the frequency converter device set forth in the seventh aspect of the invention.